http2/h2demo: add Autocert notification email

Add golang-dev as the Autocert notification email so Let's Encrypt can
send us emails. golang-dev is not an ideal choice, but we need something
publicly accessible and there isn't an obvious better option. My
understanding is we should expect essentially no emails so I don't want
to worry too much about it.

Updates golang/go#47108.

Change-Id: Ic3b5b7554d516ea2840bb56499eb3b8f35bf2304
Reviewed-on: https://go-review.googlesource.com/c/net/+/334929
Trust: Heschi Kreinick <heschi@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/http2/h2demo/h2demo.go b/http2/h2demo/h2demo.go
index f8e0019..8ac8d71 100644
--- a/http2/h2demo/h2demo.go
+++ b/http2/h2demo/h2demo.go
@@ -491,6 +491,7 @@
 		Prompt:     autocert.AcceptTOS,
 		HostPolicy: autocert.HostWhitelist("http1.golang.org", "http2.golang.org"),
 		Cache:      autocertcache.NewGoogleCloudStorageCache(storageClient, "golang-h2demo-autocert"),
+		Email:      "golang-dev@googlegroups.com", // for lack of a better choice.
 	}
 
 	errc := make(chan error, 2)